OK, so what if we expanded this inquiry not just to former Presidents, but to the current and future Presidents, too? In other words, when were the most number of men alive who, at some point in time either before or after that time, became President of the U.S.? Before checking, let's think some. It's obviously not going to be right at the beginning, and it also wouldn't be any time in the very recent past, because there are at least several people walking this earth who will be President some time in the future whom we don't know about yet. And while life spans increased during the 20th century, so did the length of Presidential administrations; there were 23 Presidents from 1801 to 1901, and only 17 from 1901 to 2001.

Wikipedia comes in handy again, this time with a timeline. They don't tally things up for us, but if you go through and add things up, you can figure out that there were four periods of time when there were 18 men living who at some point in time had or would become President of the United States: